nestjs-patterns

SKILL.md

NestJS Development Patterns

Production-grade NestJS patterns for modular TypeScript backends.

When to Activate

Building NestJS APIs or services

Structuring modules, controllers, and providers

Adding DTO validation, guards, interceptors, or exception filters

Configuring environment-aware settings and database integrations

Testing NestJS units or HTTP endpoints

Project Structure
src/
├── app.module.ts
├── main.ts
├── common/
│   ├── filters/
│   ├── guards/
│   ├── interceptors/
│   └── pipes/
├── config/
│   ├── configuration.ts
│   └── validation.ts
├── modules/
│   ├── auth/
│   │   ├── auth.controller.ts
│   │   ├── auth.module.ts
│   │   ├── auth.service.ts
│   │   ├── dto/
│   │   ├── guards/
│   │   └── strategies/
│   └── users/
│       ├── dto/
│       ├── entities/
│       ├── users.controller.ts
│       ├── users.module.ts
│       └── users.service.ts
└── prisma/ or database/

Keep domain code inside feature modules.

Put cross-cutting filters, decorators, guards, and interceptors in common/.

Keep DTOs close to the module that owns them.

Bootstrap and Global Validation

async function bootstrap() {
  const app = await NestFactory.create(AppModule, { bufferLogs: true });

  app.useGlobalPipes(
    new ValidationPipe({
      whitelist: true,
      forbidNonWhitelisted: true,
      transform: true,
      transformOptions: { enableImplicitConversion: true },
    }),
  );

  app.useGlobalInterceptors(new ClassSerializerInterceptor(app.get(Reflector)));
  app.useGlobalFilters(new HttpExceptionFilter());

  await app.listen(process.env.PORT ?? 3000);
}
bootstrap();

Always enable whitelist and forbidNonWhitelisted on public APIs.

Prefer one global validation pipe instead of repeating validation config per route.

Modules, Controllers, and Providers

@Module({
  controllers: [UsersController],
  providers: [UsersService],
  exports: [UsersService],
})
export class UsersModule {}

@Controller('users')
export class UsersController {
  constructor(private readonly usersService: UsersService) {}

  @Get(':id')
  getById(@Param('id', ParseUUIDPipe) id: string) {
    return this.usersService.getById(id);
  }

  @Post()
  create(@Body() dto: CreateUserDto) {
    return this.usersService.create(dto);
  }
}

@Injectable()
export class UsersService {
  constructor(private readonly usersRepo: UsersRepository) {}

  async create(dto: CreateUserDto) {
    return this.usersRepo.create(dto);
  }
}

Controllers should stay thin: parse HTTP input, call a provider, return response DTOs.

Put business logic in injectable services, not controllers.

Export only the providers other modules genuinely need.

DTOs and Validation

export class CreateUserDto {
  @IsEmail()
  email!: string;

  @IsString()
  @Length(2, 80)
  name!: string;

  @IsOptional()
  @IsEnum(UserRole)
  role?: UserRole;
}

Validate every request DTO with class-validator.

Use dedicated response DTOs or serializers instead of returning ORM entities directly.

Avoid leaking internal fields such as password hashes, tokens, or audit columns.

Auth, Guards, and Request Context

@UseGuards(JwtAuthGuard, RolesGuard)
@Roles('admin')
@Get('admin/report')
getAdminReport(@Req() req: AuthenticatedRequest) {
  return this.reportService.getForUser(req.user.id);
}

Keep auth strategies and guards module-local unless they are truly shared.

Encode coarse access rules in guards, then do resource-specific authorization in services.

Prefer explicit request types for authenticated request objects.

Exception Filters and Error Shape

@Catch()
export class HttpExceptionFilter implements ExceptionFilter {
  catch(exception: unknown, host: ArgumentsHost) {
    const response = host.switchToHttp().getResponse<Response>();
    const request = host.switchToHttp().getRequest<Request>();

    if (exception instanceof HttpException) {
      return response.status(exception.getStatus()).json({
        path: request.url,
        error: exception.getResponse(),
      });
    }

    return response.status(500).json({
      path: request.url,
      error: 'Internal server error',
    });
  }
}

Keep one consistent error envelope across the API.

Throw framework exceptions for expected client errors; log and wrap unexpected failures centrally.

Config and Environment Validation

ConfigModule.forRoot({
  isGlobal: true,
  load: [configuration],
  validate: validateEnv,
});

Validate env at boot, not lazily at first request.

Keep config access behind typed helpers or config services.

Split dev/staging/prod concerns in config factories instead of branching throughout feature code.

Persistence and Transactions

Keep repository / ORM code behind providers that speak domain language.

For Prisma or TypeORM, isolate transactional workflows in services that own the unit of work.

Do not let controllers coordinate multi-step writes directly.

Testing

describe('UsersController', () => {
  let app: INestApplication;

  beforeAll(async () => {
    const moduleRef = await Test.createTestingModule({
      imports: [UsersModule],
    }).compile();

    app = moduleRef.createNestApplication();
    app.useGlobalPipes(new ValidationPipe({ whitelist: true, transform: true }));
    await app.init();
  });
});

Unit test providers in isolation with mocked dependencies.

Add request-level tests for guards, validation pipes, and exception filters.

Reuse the same global pipes/filters in tests that you use in production.

Production Defaults

Enable structured logging and request correlation ids.

Terminate on invalid env/config instead of booting partially.

Prefer async provider initialization for DB/cache clients with explicit health checks.

Keep background jobs and event consumers in their own modules, not inside HTTP controllers.

Make rate limiting, auth, and audit logging explicit for public endpoints.